/* 
 * mmdecode.c -- a tool for decoding QP/BASE64 string
 *					deliver from Maple 3
 * 
 * of SEEDNetBBS generation 1 (libBBS implement)
 *
 * Copyright (c) 1998, 1999, Edward Ping-Da Chuang <edwardc@edwardc.dhs.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * CVS: $Id: mmdecode.c 366 2007-05-12 16:35:51Z danielfree $
 */

/*-------------------------------------------------------*/
/* lib/str_decode.c	( NTHU CS MapleBBS Ver 3.00 )	     */
/*-------------------------------------------------------*/
/* target : included C for QP/BASE64 decoding		     */
/* create : 95/03/29				 	                 */
/* update : 97/03/29				 	                 */
/*-------------------------------------------------------*/


/* ----------------------------------------------------- */
/* QP code : "0123456789ABCDEF"				             */
/* ----------------------------------------------------- */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define	IS_QP		0x01
#define	IS_BASE64	0x02
#define	IS_TRAN		0x04

static int qp_code(register int x)
{
    if (x >= '0' && x <= '9')
        return x - '0';
    if (x >= 'a' && x <= 'f')
        return x - 'a' + 10;
    if (x >= 'A' && x <= 'F')
        return x - 'A' + 10;
    return -1;
}


/* ------------------------------------------------------------------ */
/* BASE64 :							      */
/* "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" */
/* ------------------------------------------------------------------ */


static int base64_code(register int x)
{
    if (x >= 'A' && x <= 'Z')
        return x - 'A';
    if (x >= 'a' && x <= 'z')
        return x - 'a' + 26;
    if (x >= '0' && x <= '9')
        return x - '0' + 52;
    if (x == '+')
        return 62;
    if (x == '/')
        return 63;
    return -1;
}


/* ----------------------------------------------------- */
/* judge & decode QP / BASE64				 */
/* ----------------------------------------------------- */


void _mmdecode(unsigned char *str)
{
    int code, c1, c2, c3, c4;
    unsigned char *src, *dst;
    unsigned char buf[256];

    src = str;
    dst = buf;
    code = 0;

    while (c1 = *src++)
    {
        if (c1 == '?' && *src == '=')
        {
            if (code)
            {
                code &= IS_TRAN;
                if (*++src == ' ')
                    src++;
            }
            continue;
        }

        if (c1 == '\n')		/* chuan: multi line encoding */
            goto line;

        if (code & (IS_QP | IS_BASE64))
        {
            if (c1 == '_')
            {
                *dst++ = ' ';
                continue;
            }

            if ((c1 == '=') && (code & IS_QP))
            {
                if (!(c1 = *src))
                    break;

                if (!(c2 = *++src))
                    break;

                src++;
                *dst++ = (qp_code(c1) << 4) | qp_code(c2);
                code |= IS_TRAN;
                continue;
            }

            if (code & IS_BASE64)
            {
                c2 = *src++;

                if (c1 == '=' || c2 == '=')
                {
                    code ^= IS_BASE64;
                    continue;
                }

                if (!(c3 = *src++))
                    break;

                if (!(c4 = *src++))
                    break;

                c2 = base64_code(c2);
                *dst++ = (base64_code(c1) << 2) | ((c2 & 0x30) >> 4);

                if (c3 == '=')
                {
                    code ^= IS_BASE64;
                }
                else
                {
                    c3 = base64_code(c3);
                    *dst++ = ((c2 & 0xF) << 4) | ((c3 & 0x3c) >> 2);

                    if (c4 == '=')
                        code ^= IS_BASE64;
                    else
                        *dst++ = ((c3 & 0x03) << 6) | base64_code(c4);
                }

                code |= IS_TRAN;
                continue;
            }
        }

        /* "=?%s?Q?" for QP, "=?%s?B?" for BASE64 */

        if ((c1 == '=') && (*src == '?'))
        {
            c2 = 0;

            for (;;)
            {
                c1 = *++src;
                if (!c1)
                    goto home;

                if (c1 == '?')
                {
                    if (++c2 >= 2)
                        break;

                    continue;
                }

                if (c2 == 1)
                {
                    if (c1 == 'Q')
                        code = IS_QP;
                    else if (c1 == 'B')
                        code = IS_BASE64;
                }
            }

            src++;
            continue;
        }

        *dst++ = c1;
    }

home:

    if (code & IS_TRAN)
    {
line:
        *dst = '\0';
        strcpy(str, buf);
    }
}
